1. Field of the Invention
The present invention relates to a data structure for performing recording on a disk recording medium such as an optical disk, a magnetic disk or the like, a disk recording device and a reproducing device for recording/reproducing information signals by using this disk recording medium and the methods thereof.
2. Description of the Related Art
An optical disk drive which is one of disk drives is utilized as the external storage device of various computers and a document filing device, and further as a large capacity storage device for storing information on static and moving images. In an optical disk, a track on which recording is to be made is predetermined and each track is divided into a plurality of sectors. Each sector includes an area on which corresponding track numbers and sector numbers are prerecorded, a data area on which information signals are recorded and an error correction area.
The data structure of a usual optical disk is shown in FIGS. 1A and 1B. FIG. 1A is a view showing a track form in the optical disk while FIG. 1B is a view showing the data structure stored in one sector. As shown in FIG. 1A, the optical disk is helically formed having a plurality of tracks with one track made by one round starting from the outermost periphery. One track, in turn, is divided into a plurality of sectors (e.g., eight sectors in the case of FIG. 1A). Further, as shown in FIG. 1B, each sector includes an ID area on which track numbers and sector numbers are recorded, a SYNC area for synchronizing, a data area for storing real data and an ECC area for storing error checking codes.
The error rate of the optical disk itself is 10.sup.-5 to 10.sup.-6, larger than that (10.sup.-11 to 10.sup.-12) generally required by an information storage device. Thus, in the conventional optical disk drive, a required error rate is met by using error correction codes. Moreover, there is little influence by small damages and dirt in the optical disk drive, since a protecting layer, to which the dirt and damages of the optical disk are stuck, and an information recording face are separated and data is interleaved for dispersing continuous errors (burst error). Therefore, in normal recording/reproducing, there are no practical problems generated using the error correction codes. However, when there is a decline in quality of the optical disk due to the long time retaining thereof or when there are a great amount of dirt and damages thereto, errors exceeding the performance of the error correction codes may be generated at the time of reproducing and thus the information signals cannot be correctly reproduced.
Given such a situation, in the case of a sector where the number of errors is increased to a certain extent within the range not exceeding the performance of the error correction codes, another sector is allocated by terminating the use thereof thereafter and the method of a replacement sector for transferring information to the sector is used. When errors exceeding the performance of the error correction codes are generated even by this method, however, the recorded information signals cannot be correctly reproduced and thus they cannot be transferred to the replacement sector. For example, when the error correction codes capable of correcting eight errors are used, error correction cannot be performed if there are nine or more errors, making it impossible to obtain correct information signals.
Further, as it is most often the case that the replacement sector is, for instance, set in a track on the outermost or the innermost periphery, the number of accessing times (the number of times for moving an optical head to a targeted track or a sector) is increased, thereby lengthening reproducing time. As an example, if an information signal A is recorded in the first to fourth sectors of the first track and the replacement sector is in the tenth track, first the optical head is moved to the first track and then the information signals recorded in the first to fourth sectors are read in order to reproduce the information signal A. Therefore, the number of accessing times not needing the replacement sector is one.
In the following reference is made to a case where the replacement sector is allocated because of the increase of errors generated by dirt and damages to the optical disk in the third sector of the first track and the information signal recorded in the third sector is moved to the first sector of the tenth track which is the replacement sector. In this case, at the time of reproducing the information signal A, first the optical head is moved to the first track and then the information signals recorded in the first to second sectors are read. Subsequently, the optical head is moved to the tenth track and the information signal recorded in the first sector, which is replacement sector, is head. Thereafter, the optical head is moved to the first track and the information signal recorded in the fourth sector is head. The information signal A is reproduced by means of this operation. The number of accessing times in this case is three, thereby lengthening the period of time for reproducing the information signal A.
When the transfer of the information signals to the replacement sector is increased as described above, the period of time for recording and reproducing the information signals is lengthened. Ideally, the transfer of the information signals to the replacement sector must be performed when errors exceeding the performance of the error correction codes are generated. However, since the information signals cannot be correctly reproduced after errors exceeding the performance thereof are generated, it is impossible to transfer the information signals to the replacement sector. Moreover, since a transferring speed is greatly reduced if there is transfer of the information signals to the replacement sector, it is practically impossible to use the replacement sector in reproducing information on moving images which requires a high transferring speed.
In order to solve the above-mentioned problems, it may be conceivable, for instance as shown in FIG. 2, to calculate n-1 pieces of sector parities within one track and to record these parities as parity sectors. In the example of FIG. 2, one track is constituted of n-1 pieces of information sectors and one parity sector and for instance, the exclusive OR of the information signals recorded in the first to the n-1th information sectors of the track number N is recorded in the parity sector thereof. Though in this parity sector error correction is allowed up to one sector per one track, it is not so efficient because one parity sector is set for every one track, and if n=11, for instance, the ratio of the party sector to the total amount of information recorded on the optical disk is 9%. FIG. 3 shows the example where one parity sector is provided per two tracks based on the above consideration. In this case, if n=11 likewise, the ratio of the parity sector to the total amount of information is 4.5%, half that shown in FIG. 2.
In a case where there are conspicuous dirt and damages to the optical disk, however, a plurality of sectors may be affected. Consequently, burst errors may be generated over a plurality of sectors adjacent to one another in the circumferential and track directions of the optical disk. The optical disks having such large damages and great deal of dirt are eliminated as defective products at the time of shipping. It is possible, however, that even good products at the time of shipping may be damaged and given dirt during practical use though frequencies differ depending on environments for use. In a parity sector where error correction is performed only for one sector per one track or one sector per two tracks as shown in FIG. 2 or 3, such burst errors may not be dealt with. Though it is possible to increase the number of sectors per one track to be corrected by increasing the number of parity sectors, the amount of information to be recorded is decreased.
As described above, in the conventional technique using error correction codes and parities, in a case where errors exceeding the performance of the error correction codes are generated by a decline in quality of a disk due to the long time retaining thereof, a great amount of dirt and damages thereto, or the like at the time of reproducing, the information signals cannot be correctly reproduced and by the method of increasing the number of sectors per one track to be corrected by increasing the number of parity sectors the amount of information signals to be recorded is decreased.